1. Field of the Invention
The present invention relates to a method of manufacturing a cushion material having different hardnesses which is used for a vehicle seat, a bed, or the like.
2. Description of the Related Art
As illustrated as an example in FIG. 6, when a cushion material is used for a seat pad 70 of a seat cushion for a vehicle, the hardness of a central portion on 70A of the seat pad 70 is low, and the hardness of both side portions 70B is high so as to improve the seating comfort for the vehicle occupant and to improve the ability of the seat pad 70 to hold the vehicle occupant.
An example of a method of manufacturing such a cushion material having different hardnesses in different portions is disclosed in Japanese Patent Application Laid-Open No. 3-170112.
As illustrated in FIG. 7, in this conventional method of manufacturing a cushion material, when a plurality of heat-fusible fibers, which are shaped as cotton balls, are blown into a mold 72, cotton ball shaped heat-fusible fibers 74A (the black fibers in the drawing), which are hardened to an appropriate degree by a binder in advance, are mixed and blown in together with cotton ball shaped heat-fusible fibers 74B (the white fibers in the drawing), which are not bound by a binder, at a portion 72A within the mold 72 which corresponds to a central portion of the seat pad, i.e., at a portion which is to be formed soft. The heat-fusible fibers 74A and 74B are mixed such that the density of the heat-fusible fibers 74A is higher at portions 72B corresponding to both side portions of the seat pad, i.e., at portions which are to be formed hard. Thereafter, pressure is applied as illustrated in FIG. 8.
Subsequently, as illustrated in FIG. 9, the mold 72 which is filled with the heat-fusible fibers is placed within a heating portion 86 of a penetration-type heating apparatus 84 which is equipped with a hot air generating device 80 and a fan 82. The entire mold is heated at the same temperature.
However, in this method of manufacturing a cushion material, the process for manufacturing the cotton ball shaped heat-fusible fibers 74A and 74B is complicated. Further, in order to form the respective hard portions and soft portions of the cushion material by manipulating the mixing ratio of the heat-fusible fibers 74A and the heat-fusible fibers 74B, it is necessary to mix the heat-fusible fibers 74A and the heat-fusible fibers 74B uniformly in accordance with the respective soft portions and hard portions. This process is extremely difficult, and irregularities in hardness due to irregularities in the densities of the fibers occur easily.